Electromagnetic switch.



ELECTROMAGNETIC SWITCH.

APPLICATION FILED NOV. 20. i914.

Patented Nov. 9, 1915.

mu mull INVENTDR: JAMES J. Wcmo,

H15 ATTORNEY UNITED STATES PATENT OFFICE.

JAMES J". WOOD, OF FORT WAYNE, INDIANA, ASSTGNOR T0 GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

ELECTROMAGNETIC SWITCH.

To all whom it may concern:

Be it known that 1, JAMES J. WOOD, a citizen of the United States, residing at Fort 'Wayne, county of Allen, State of Indiana, have. invented certain new and useful Improvements in Electromagnetic Switches, of which the following is a specification. p This invention relates to electromagnetic switches for the control of electric circuits and has for its object the provision of improved means whereby an electric circuit may be controlled in a reliable, simple-'and etlicient manner. 1

My invention relates more specifically to electromagnetic switches for controlling electric motor circuits, one of the objects being to provide a device of this character which will effect the automatic starting of the motor under the control of the motor current.

In the operation of electric motors it is common to both start the motor and control its speed by means of a resistance which is cut in and out of circuit. Every time a section of resistance is cutout the current temporarily rises above normal value. The increase in speed which is caused by the cutting out of the section of resistance immediately reduces the current. During the starting of the motor, therefore, there is a temporary rush of current for each section of resistance which is cut out.- These sections are frequently cut out of circuit by electromagnetic switches which operate automatically in succession. In orderto prevent the switches from operating too rapidly and increasing the current beyond a safe value, various means have been devised. An ideal switch for this purpose is one contain: ing a winding which carries the motor current and a switch member. controlled thereby for cutting out the resistance, the arrangement being such that the switch member will not be operated to cut out the resistance until the current has fallen to a predetermined value and will assume an open position when the winding is deenergized. A switch of this character was invented by Vi alter O. Lum and forms the subject matter of an application. Serial No. 611,151, filed l ebruary 27, 1911, assigned to the same assignee as this application.

While the broad features of my device are described and claimed in the said Lum ap- Specification of Letters Patent.

Patented Nov. 9, 1915.

Applicationfiled November 20, 1914. Serial No. 873.211.

plication, the more specific features thereof constitute important improvements which lend themselves to efficiency of operation and also make the device more accurate and positive in operation. Likewise, the improved mechanical construction of the switch renders it more rugged and compact and likewise decreases the cost of production.-

In the accompanying drawings illustratmg one form of my'invention, .Figure 1 is a side elevation of a complete electromagnetic switch embodying my improvements; Fig. 2 is a front elevation of'the same; Figs. 3, 4 and 5 show. in outline the various positions which the switch assumes.

Referring to Figs. 1 and 2, 10 represents an energizing winding for magnetizing the magnetic structure composed of an upper pole piece 11 and a lower polepiece 12 connected by a core 13. These parts, together with the winding 10 mounted upon the core, form anelectromagnet which is secured to an insulating base 1 1. A fixed contact 15 is also secured to the insulating base adjacent the magnet so as to cooperate with the moving contact as hereinafter described. A switch lever 16, which is provided at its upper end "with a contact 17 to cooperate with the stationary contact 15, is pivoted at 18. These contacts 15 and 17 are shaped so as to wipe or roll upon each other in a manner now well understood in the art, and to this end the contact 17 is mounted upon a pivoted bracket 19 which is spring pressed by means of a spring 20 to move the contact to cooperate with both the upper polepiece 11 and the lower polepiece 12. The upper )ole iece 11 is'enlar ed so as to afford a Wide face and the upper end of the lever 16 is similarly formed so as to hold by the polepiece across the gap 22 which may be called the closing gap. The lever 16 is pivoted to the bracket 23, preferably of brass or other non-magnetic material, which bracket is pivoted at 24 to the magnetic frame. The inner end of the bracket 23, which is in the form of a bell crank lever is pressed downward by a spring 31 interposed between the end of the bracket and the head of a scre 25 which passes through the spring and is screwed into the magnetic frame. The

lower end of the lever 16 coiiperates with the polepiece 12, which is also enlarged to give an effective pull across the gap 26,

which may be called the holding out gap. 1

have shown this lever curved at its lower end and terminating in a flat surface 27 which cotiperates with a flat surface 28on the polepiece 12, as shown. These two faces 27 and 28 are in contact when the switch is closed so as to form a closed magnetic circuit. There is also some attraction during the closing movement between these pole faces 27 and 28 across the gap 29 which constitutes an auxiliary closing gap. The'pivotal point of the switch lever 16 is adjacent to the upper end and the spring normally forces the bracket to the position shown in Figs. '1 and 3, in which position the upper end of the lever is forced outward from the polepiece to its maximum distance. The switch lever and the attached parts are so located, and they weight is so distributed around the pivot that the lower end of the lever normally bears against the polepiece 12, there being an adjusting screw 30 for adjusting the gap between the lower end of the lever and the polepiece. The face 16 of the upper end of the lever in the normal position' of the latter is at such an. angle with the face of the polepiece 11 that when the pivot 18 is moved inward by the attraction across. the gap 22 the lower end'of the armature portion of the face 16 engages the polepiece 11 and acts as' a fulcrum at 22.

The lever 16 now turns on this fulcrum about the pivot 18 whenit is moved to its closed position by the pressure of the spring 31 supplemented by the pull across the gap 22and the slight pull across gap 29.

As thus constructed anda-rrafnged,the operation of my device is as' follows: Normally the parts are in the position, shown in Figs. 1 and 3. lVhen the winding is energized above a predetermined value the upper end of the lever 16 will be moved inward until the lower end of the face 16 touches the polepiece 11, the lower end of the lever during this movement being held in contact with polepiece 12., In this movement, the bracket 23 is turned about. its pivot 24 and compresses the spring 31. It will benoted that the tendency of thelower end of the lever to move isrelatively; small due to the long leverage at which theholdingout force at that end acts. This leverage is about equal to the distance between the pivot 18 and the screw 30. This condition exists until the lower, end of pole face 16' touches pole piece 11.. The switch will therefore be held open during thisinit'ial movement due'to a current above the predetermined value atwhich-theswitch'is designed to close. :As the gap. -i22.=clo-ses more flux willpass into thelever 16 and-hence more flux will cross the lower gap 26 and true that the flux is also increasing across the auxiliary gap 29 but this gap is so wide as to have little effect at this time. The

switch will now remain in the position shown in Fig. 4, while the winding is energized at the high current value. There are now three forces tending to close the switch. One of these forces is mechanical due to the pressure of the spring 31 which is exerting a force on pivot 18 tending. to turn the switch lever around the fulcrum 22.

There is also a very substantial magnetic pull acrossthe gap 22 acting on the opposite side of the fulcrum 22 from thepivot. The third force-tending to close the switch is the magneticv pull across the auxiliary gap 29, but this is relatively small. The holding out force is that due to the attraction across the holding out gap 26. The arrangement is such that the electromagnetic holding out force will be greater than the forces tending to close the switch when the current is a ove a predetermined value. If new the current should drop to the predetermined value at which the switch is designed to close, the switch lever will be moved to the closed position shown in Fig. 5. This is due to the fact that as the current decreases the total flux decreases so that the pull across the holding out gap as well :as the pull across the closing gaps, decreases, while the force due to the compression of the spring remains constant. There'must come a time, therefore, as the flux decreases when the closing force, which includes a constant force, will overcome the holding out force which isdecreasing. 'lVhen the proper current value is reached the closing force overpowers the holding out force and as the switch member starts to move to closed position the holding out gap 26 isincreased, while the closing gap is decreased so that the closing magnet-icforces increase rapidly until finally the switch lever is pulled strongly against the polepiece 11 and wipes the contacts 15 and 17 on each other, as shown in Fig. 5. Y

The current value at which the switch closes may be adjusted over a wide range by turning the screw30. The turning of this screw varies the air gap which, of course, varies the holding out force for a, given excitation. Ifthe holding out gap is wider the switch will close at a higher value, and vice versa, if the gap is narrow the switch will close at a lower value. Upon a rush of current above the value at which the switch is adjusted to close the switch will remain open and will close when the current drops to that value.

. W hile I have described my invention in concrete form and as operating in' a specific manner in -'accordance'"with. the patent statutes, it should be understood that I do not limit my invention thereto as various modifications thereof will suggest themselves to those skilled in the art without departing from the spirit of my invention, the scope of which is set forth in the annexed claims.

What I claim as new and desire to secure by Letters Patent of the United States,is

1. An electromagnetic switch comprising a magnetizing winding, a magnetic structure having two polepieces, a switch lever ':Forming a closing gap and a holding out gap at said polepieces and normally in open position against the polepiece at the holding out gap, and a movable spring pressed pivot for said lever located between said polepieces adjacent the polepiece at the closing gap, said pivot being movable against the spring tension to cause the lever to engage the polepiece and form a fulcrum at the closing gap when the winding is energized above a predetermined value.

2. An electromagnetic switch comprising a magnetizing winding, a magnetic structure, a switch lever normally in open position, and a spring pressed element pivotally supporting the switch lever so as to form closing gap and a holding out gap in said structure, said lever being movable by attraction across the closing gap to place the spring under tension so that the sp'ring wil'l tend to move the switch member to closed position against the pull at the holding out gap when the winding is energized above a predetermined value.

3. An electromagnetic switch comprising a magnetizing winding, a magnetic structure including apivoted switch lever having a closing gap and a holding out gap in said structure, and a spring normally pressing the pivot of said switch member to cause the latter to assume an open position, said spring being compressed upon the energization of the winding above a predetermined value by the pull across the closing gap to.

give the member a tendency to close against the pull of the holding out gap.

4. An electromagnetic switch comprising a magnetizing winding, a magnetic structure having two polepieces, a switch lever having a closing gap and a holding out gap at said polepieces, and a movable element a magnetizing winding, a magnetic strueture, a switch lever having a closing gap and a holding out gap in said structure, and a movable element. forming, a pivotal support between said gaps for said switch lever and normally spring pressed to move the switch lever to open position said lever being movable by attraction across the closing gap to place the spring under tension and form .a fulcrum on the opposite side of the pivot fromithe holding out gap so that the spring will tend to move the switch member to closed position against the pull at the holding out gap when the winding is energizedabove apredetermined value.

.(3'. 7 An, electromagnetic switch comprising switch lever having a closing gap and a '--.-l.1olding'out gap in said structure pivoted to ,the'supp'ortso that the holding out gap acts upon the lever with a greater leverage than that of the closing gap, said supporting ele ment'being spring pressed so as to normally move the switch lever to open position and movable-by attraction across the closing gap to-place the spring under tension and form a fulcrum on the opposite side of the pivot from the holding out gap whereby the spring will tend to move the switch member to closed position against the pull at the f holding out gap when the winding is energized above a predetermined value.

In witness whereof, I have hereunto set my hand this 14th day of November 1914'.

JAMES J. WOOD.

\Vitnesses H. E.-Rnnvns, L. M. GORMAN.

Copies of this patent may be obtained for-five cents each, by addressing the Commissioner of Patents, Washington, D. C. 

